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Old 12-20-05, 02:24 AM   #1
gundi61
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Join Date: Dec 2005
Posts: 1
Default 1280x720@50Hz with nforce2

Hello!

I'm trying to get my LCD-TV working via the VGA-port with it's native resolution 1280x720@50Hz.
My GPU is an onboard nForce2 Chipset (Geforce4 MX).

So, my first try was to use the common 720p50-timing:

Modeline "720p50" 74.250 1280 1680 1800 1980 720 725 730 750

1)
Because the nvidia-Driver/-GPU only accepts HTotals divisible by 8, i have to use a HTotal of 1976 or 1984.
Unfortunately, with 1976 the picture has a slight overscan and 1984 has a slight underscan (approx. 4 Pixels) horizontally on my LCD-TV (=> no pixelmapping ) . The TV seems to be optimized for 1980 HTotal.
Any solution known to this problem with nVidia-GPU's?

2)
Also, i've problems to match a 50 Hz refreshrate exactly (for PAL-TV).
Using the following modeline:

Modeline "720p50" 74.250 1280 1680 1800 1976 720 725 730 750

i'm getting a refreshrate (mathematically) of 50,1 Hz, which results in some stuttering during PAL-replay.

But adjusting the Pixelclock to 74,1 Mhz:

Modeline "720p50" 74.100 1280 1680 1800 1976 720 725 730 750

mathematically resulting in an exact 50 Hz refreshrate, the stuttering is also present.
So i'm wondering, wether the GPU matches the pixelclock of 74,1 MHz exactly, or does the chip/driver change the wanted pixelclock to something other which the chip is able to?
In other words: Can I set the pixelclock to any value or are there discrete steps for altering the pixelclock?

Greetings from germany
Guido
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